1. General

1.1 Different modes of friction

Since Stribeck's work, possible bearing operating regimes have been classified into four main types:

• the friction regime without the interposition of a liquid lubricant ;

• limit lubrication speed ;

• mixed lubrication ;

• the hydrodynamic lubrication regime.

In practice, the characterization most frequently adopted to differentiate between different bearing operating regimes is based on the study of the curve giving the overall coefficient of friction of the system as a function of the following parameters: the speed of relative displacement between the two opposing surfaces,...